Fiber lasers and amplifiers are being used in a growing number of applications. As these mature in the commercial, deployment, an intense focus is being put on their reliability and that of their components. With the current progress in this field, reliability demonstrations must be made at increasingly higher power levels. Optical fiber reliability, connector reliability and susceptibility of optical fiber coatings to optical power damage have been studied for a number of years. Power levels for most applications have however been limited to the range of a few tens of Watts.
In U.S. Pat. No. 4,678,273 a high power optical fiber with improved covering is described. In U.S. Patent Application Publication No. 2004/0175086 a fiber with a multilayer cladding arrangement is proposed to provide means of extracting energy from the cladding. These two inventions specifically address the issue of power handling of the optical fiber and its coating, but do not provide a solution for the component related power handling issues. In U.S. Pat. Nos. 5,291,570 and 5,946,437, there are described two variants of high power fiber connectors with means to prevent intense radiation, not coupled in the optical fiber, from damaging the fiber jacket. These two patents propose no solution to the specific problem of fiber component packaging and describe only a solution applicable to the ends of fibers where light is coupled from a source to the fiber input. In U.S. Pat. No. 6,865,316 B1, a cladding mode stripper is described for use in dissipating unwanted optical power coupled to the fiber cladding in a laser-to-fiber coupling arrangement. This patent is another example of an invention addressing excess light at the launch point into a fiber. In U.S. Patent Application Publication No. 2003/0103724, a fiber termination is proposed for lessening negative effects associated with launching high power signals from a single mode optical fiber. This is the reverseproblem from optical launch into the fiber and does not cover fiber component related high power issues.
In U.S. Pat. No. 6,860,651 B2, a fiber optic component packaging invention is presented where various configurations are claimed to optically extract lost light to displace heat generation away from the optical device. The principal claim of this invention is to use a fiber to capture and divert optical power loss into a terminated end, where more efficient heat dissipation means can be applied. This solution is better suited for a certain class of components where the lost signal is available for coupling to a fiber, for example in micro-optic thin film components where optical loss is available in the form of a well defined reflected portion of the input beam. This is not generally the case in fiber optic components. In general optical loss will be spurious in nature and the corresponding optical beam characteristics will be ill-defined, which makes the use of an optical fiber based loss extraction impractical.
All-fiber components, such as tapered fused bundle ('11'13) couplers, pump strippers, splices, mode field adaptors and Bragg gratings, allow monolithic integration of fiber laser and amplifier devices for deployment in the field. Characterized by intrinsically low loss transmission, they are well suited to handle signal and pump light, which are likely to reach the kW level in the near future. However, little progress has been made or improvements proposed for increasing the power handling capabilities of these components. In general, several package features are dictated by the requirements to robustly enclose the component in a protective enclosure, decouple the optical device from loads applied to the lead fibers and maintain performance in an uncontrolled environment, where temperature and humidity variations can lead to aging or thermally induced stresses. These requirements must be met while reducing the package sensitivity to high optical power levels, which creates a need for a novel packaging solution.